security/libgcrypt: Fix armv6 build

Armv6 fails to build jitterentropy-base.c without optimization,
even though #pragma GCC optimization and #pragma clang optimization
are specified. For now brute force disable building the jitter
entropy generator on armv6.

PR: 253698
Submitted by: yani _ pi-greece.eu
Reported by: yani _ pi-greece.eu